1. Field of the Invention
The present invention relates to an improvement of a color image pickup device.
2. Description of the Prior Art
A color image pickup device of a type, for example, as shown in FIG. 1, in which a stripe filter consisting of a repeated arrangements of the R(red), the Cy(cyan) and the G(green) filters are provided in front of the light sensing part of the solid image pickup element, wherein each color filter is made to correspond to each of pitches of the picture elements of the image pickup element, is known.
When the horizontal reading out clock frequency of the image pickup element having such a filter as described above is let to be fR, there exists a carrier of each color signal in a deviated state, as shown in FIG. 2, wherein the phase is deviated by 2/3.pi. at the position of 1/3 fR.
When the synthetic optical characteristics of a system comprising image pickup elements, color filters and so on are set in such a manner that the output of the image pickup element can be obtained evenly for every color component when an object image with zero color saturation is picked up, the vectors of the side wave band signals of individual colors at 1/3 fR in FIG. 2 are compensated by each other so that there takes place no inclusion of the side wave band component into the base band component used as the brightness signal, the so-called "Folding noise".
Although originally such a balance effect is obtained only for a colorless object, the signals are practically treated in a band of frequency higher than the Nyquist's frequency for each color signal because the color saturation of the picked up object image is normally low.
However, when an object with high color balance is in the picture, the sampling frequency is lowered to 1/3 fR so that the Nyquist's frequency is also lowered to 1/6 fR. Thus, for the object image having a spacial frequency component above 1/6 fR, there takes place a folding noise, which deteriorates the picture quality.
On the other hand, it is known that, visually, not so great a resolution power is required for an object with high color saturation.